2 Introduction- ResourcesRecommendations for the Standardization and Interpretation of the Electrocardiogram. J. Am. Coll. Cardiol. 2007;49;

3 I n the century since the introduction of the string galvanometer by Willem Einthoven, the electrocardiogram (ECG) has become the most commonly conducted cardiovascular diagnostic procedure and a fundamental tool of clinical practiceHistory

4 the diagnosis and prompt initiation of therapy in patients with acute coronary syndromesthe most accurate means of diagnosing intraventricular conduction disturbances and arrhythmias.recognition of electrolyte abnormalities, particularly of serum potassium and calcium,the detection of some forms of genetically mediated electrical or structural cardiac abnormalities.monitor patients treated with antiarrhythmic and other drugs,preoperative assessment of patients undergoing noncardiac surgery, and inscreening individuals in high-risk occupations.Used for

8 Different leads result in different recordingsDifferent leads result in different recordings. The waves are positive and negative.The ECG machine is designed to recognise and record any electrical activity within the heart. It prints out this information on ECG paper made up of small squares 1mm squared.Each electrical stimulus takes the form of a wave and so patterns emerge made up of a number of connected waves. A standard ECG is printed at 25mm per second or 25 small squares per second (see above). In this way it is possible to calculate the duration of individual waves.10 small squares vertically is equal to 1 millivolt. So it is possible to calculate the amount of voltage being released within the heart. If the line is flat at any time in the duration of a series of waves, it indicates no electrical activity at that particular moment.The direction in which the waves point indicates whether electricity is moving towards or away from a particular lead.The general direction in which electricity normally travels through the heart is a downward diagonal line from the right shoulder to the left lower abdomen. This is because the electrical stimulus originates in the SA node (upper right side of the heart), travels through the AV node and bundle of His, and finishes mainly in the left ventricle. (remember that there is more conduction in the left ventricle).So different leads may have waves pointing in different directions. Eg. Lead AVR (right shoulder/right arm/wrist) will always see the electrical stimulus travelling away from it, therefore the waves expressed in AVR for sinus rhythm, pqrst, will all point downwards. Similarly, lead V6 (mid-left axilla, 5th intercostal space), will always see the electrical stimulus coming towards it and therefore the waves expressed in V6 for sinus rhythm, pqrst, will always be point upwards.ECG Recording

19 The standard 12-lead ECG 3 limb leads (I, II, and III),3 augmented limb leads in which theGoldberger modification of the central terminal of Wilson serves as a derived indifferent electrode that is paired with the exploring electrode (leads aVR, aVL, and aVF),6 precordial leads in which the Wilson central terminal serves as a derived indifferent electrode that is paired with the exploring electrode (V1 through V6).The standard 12-lead ECG

20 The lead connected to the right ankle is a neutral lead, like you would find in an electric plug. It is there to complete an electrical circuit and plays no role in the ECG itself.Limb Leads

23 Bipolar Leads AVr and AVl is known as lead l.AVr and AVf is known as lead llAVl and AVf is known as lead lllBipolar Leads

24 The 6 leads are labelled as "V" leads and numbered V1 to V6The 6 leads are labelled as "V" leads and numbered V1 to V6. They are positioned in specific positions on the rib cage. To position then accurately it is important to be able to identify the "angle of Louis", or "sternal angle".To find it on yourself, place your fingers gently at the base of your throat in a central position and move your fingers downward until you can feel the top of the sternum, or rib cage. From this position, continue to move your fingers downward until you feel a boney lump. This is the "angle of Louis".The angle of Louis is most easily found when the patient is lying down as the surrounding tissue is tighter against the rib cage.From the angle of Louis, move your fingers to the right and you will feel a gap between the ribs. This gap is the 2nd Intercostal space. From this position, run your fingers downward across the next rib, and the next one. The space you are in is the 4th intercostal space. Where this space meets the sternum is the position for V1.Go back to the "angle of Louis" and move into the 2nd intercostal space on the left. Move down over the next 2 ribs and you have found the 4th intercostal space. Where this space meets the sternum is the position for V2.From this position, slide your fingers downward over the next rib and you are in the 5th intercostal space . Now look at the chest and identify the left clavicle, a bone that runs from the left shoulder to the top of the sternum. The position for V4 is in the 5th intercostal space , in line with the middle of the clavicle (mid-clavicular). V3 sits midway between V2 and V4.Follow the 5th intercostal space to the left until your fingers are immediately below the beginning of the axilla, or under-arm area. This is the position for V5.Follow this line of the 5th intercostal space a little further until you are immediately below the centre point of the axilla, (mid-axilla). This is the position for V6.Now look at the picture below showing the position of the heart in relation to the rib-cage and you get an idea as to which areas are being looked at by these leads.

25 AVL is on the left wrist or shoulder and looks at the upper left side of the heart.Lead l travels towards AVL creating a second high lateral lead.AVf is on the left ankle or left lower abdomen and looks at the bottom, or inferior wall, of the heart.Lead ll travels from AVr towards AVf to become a 2nd inferior leadLead lll travels from AVL towards AVf to become a 3rd inferior lead.V2 V3 and V4 look at the front of the heart and are the anterior leads.V1 is often ignored but if changes occur in V1 and V2 only, these leads are referred to as Septal leads.V5 and V6 look at the left side of the heart and are the lateral leads.Regions of the Heart

28 The first wave (p wave) represents atrial depolarisationThe first wave (p wave) represents atrial depolarisation. When the valves between the atria and ventricles open, 70% of the blood in the atria falls through with the aid of gravity, but mainly due to suction caused by the ventricles as they expand.Atrial contraction is required only for the final 30% and therefore a relatively small muscle mass is required and only a relatively small amount of voltage is needed to contract the atria.

29 After the first wave there follows a short period where the line is flat. This is the point at which the stimulus is delayed in the bundle of His to allow the atria enough time to pump all the blood into the ventricles.As the ventricles fill, the growing pressure causes the valves between the atria and ventricles to close. At this point the electrical stimulus passes from the bundle of His into the bundle branches and Purkinje fibres. The amount of electrical energy generated is recorded as a complex of 3 waves known collectively as the QRS complex. Measuring the waves vertically shows voltage. More voltage is required to cause ventricular contraction and therefore the wave is much bigger.The QRS Complex

30 small negative wave immediately before the large QRS complexsmall negative wave immediately before the large QRS complex. This is known as a Q wave and represents depolarisation in the septum.Whilst the electrical stimulus passes through the bundle of His, and before it separates down the two bundle branches, it starts to depolarise the septum from left to right. This is only a small amount of conduction (hence the Q wave is less than 2 small squares), and it travels in the opposite direction to the main conduction (right to left) so the Q wave points in the opposite direction to the large QRS complex.The Q Wave

31 the R wave represents the electrical stimulus as it passes through the main portion of the ventricular walls. The wall of the ventricles are very thick due to the amount of work they have to do and, consequently, more voltage is required.This is why the R wave is by far the biggest wave generated during normal conduction.More muscle means more cells. More cells means more electricity. More electricity leads to a bigger wave.R Wave

32 S Wave represents depolarisation in the Purkinje fibres.The S wave travels in the opposite direction to the large R wave because, as can be seen on the earlier picture, the Purkinje fibres spread throughout the ventricles from top to bottom and then back up through the walls of the ventricles.S Wave

34 There is a brief period between the end of the QRS complex and the beginning of the T wave where there is no conduction and the line is flat. This is known as the ST segment and it is a key indicator for both myocardial ischaemia and necrosis if it goes up or down.ST Segment